Compact inverse-telephoto infrared imaging optical system

Abstract

An infrared imaging optical system includes a front lens group having negative optical power, wherein the front lens group comprises a front lens having a refractive index of from about 2.0 to about 3.0; an intermediate lens group that receives an infrared light beam from the front lens group, wherein the intermediate lens group comprises an intermediate lens having a refractive index of from about 1.35 to about 2.0; and a rear lens group having positive optical power, wherein the rear lens group receives the infrared light beam from the intermediate lens group, wherein the rear lens group comprises a rear lens having a refractive index of from about 2.0 to about 3.0, and wherein at least two of the front lens, the intermediate lens, and the rear lens have at least one aspheric surface thereon. The infrared imaging optical system further includes an infrared detector that receives the infrared light beam from the rear lens group. There is a pupil located between the rear lens group and the detector. There preferably is a cold shield around the detector having an opening therein at the pupil.

1. An infrared imaging optical system comprising:
 a front lens group having negative optical power, wherein the front lens group comprises a front lens having a refractive index of from about 2.0 to about 3.0, and wherein the front lens is not made of silicon and is not made of germanium; 
 an intermediate lens group that receives an infrared light beam from the front lens group, wherein the intermediate lens group comprises an intermediate lens; 
 a rear lens group having positive optical power, wherein the rear lens group receives the infrared light beam from the intermediate lens group, and wherein the rear lens group comprises a rear lens having a refractive index of from about 2.0 to about 3.0; and 
 an infrared detector that receives the infrared light beam from the rear lens group, wherein 
 
     the imaging optical system has a pupil located between the rear lens group and the detector. 
   
   
     2. The infrared imaging optical system of  claim 1 , wherein at least two of the front lens, the intermediate lens, and the rear lens have at least one aspheric surface thereon. 
   
   
     3. The infrared imaging optical system of  claim 1 , wherein the lenses with a refractive index of from about 2.0 to about 3.0 are made of a material selected from the group consisting of zinc sulfide, zinc selenide, arsenic trisulfide, and amtir1. 
   
   
     4. The infrared imaging optical system of  claim 1 , wherein the intermediate lens group comprises an intermediate lens having a refractive index of from about 1.35 to about 2.0. 
   
   
     5. The infrared imaging optical system of  claim 4 , wherein the lens with a refractive index of from about 1.35 to about 2.0 is made of a material selected from the group consisting of sapphire, spinel, barium fluoride, calcium fluoride, magnesium fluoride, and magnesium oxide. 
   
   
     6. The infrared imaging optical system of  claim 1 , wherein the intermediate lens group comprises an intermediate lens having a refractive index of from about 1.35 to about 1.7. 
   
   
     7. The infrared imaging optical system of  claim 1 , wherein the front lens has a refractive index of from about 2.2 to about 2.6. 
   
   
     8. The infrared imaging optical system of  claim 1 , wherein the rear lens has a refractive index of from about 2.2 to about 2.6. 
   
   
     9. The infrared imaging optical system of  claim 1 , wherein the detector is operable in a 3–5 micrometer wavelength range. 
   
   
     10. The infrared imaging optical system of  claim 1 , further including
 a cold shield around the detector and having an opening therein at the pupil. 
 
   
   
     11. An infrared imaging optical system comprising:
 a front lens group having negative optical power, wherein the front lens group comprises a front lens that is not made of silicon and is not made of germanium; 
 an intermediate lens group that receives an infrared light beam from the front lens group, wherein the intermediate lens group comprises an intermediate lens; 
 a rear lens group having positive optical power, wherein the rear lens group receives the infrared light beam from the intermediate lens group, wherein the rear lens group comprises a rear lens, and wherein at least two of the front lens, the intermediate lens, and the rear lens have at least one aspheric surface thereon; and 
 an infrared detector that receives the infrared light beam from the rear lens group, wherein the imaging optical system has a pupil located between the rear lens group and the detector. 
 
   
   
     12. The infrared imaging optical system of  claim 11 , wherein the front lens has a refractive index of from about 2.0 to about 3.0. 
   
   
     13. The infrared imaging optical system of  claim 11 , wherein the intermediate lens has a refractive index of from about 1.35 to about 2.0. 
   
   
     14. The infrared imaging optical system of  claim 11 , wherein the rear lens has a refractive index of from about 2.0 to about 3.0. 
   
   
     15. The infrared imaging optical system of  claim 11 , wherein the detector is operable in a 2–7 micrometer wavelength range. 
   
   
     16. The infrared imaging optical system of  claim 11 , further including
 a cold shield around the detector and having an opening therein at the pupil. 
 
   
   
     17. An infrared imaging optical system comprising:
 a front lens group having negative optical power, wherein the front lens group comprises a front lens having a refractive index of from about 2.2 to about 2.6; 
 an intermediate lens group that receives an infrared light beam from the front lens group, wherein the intermediate lens group comprises an intermediate lens having a refractive index of from about 1.35 to about 1.7; 
 a rear lens group having positive optical power that receives the infrared light beam from the intermediate lens group, wherein the rear lens group comprises a rear lens having a refractive index of from about 2.2 to about 2.6, and wherein at least two of the front lens, the intermediate lens, and the rear lens have at least one aspheric surface thereon; and 
 an infrared detector that receives the infrared light beam from the rear lens group, wherein the imaging optical system has a pupil located between the rear lens group and the detector. 
 
   
   
     18. The infrared imaging optical system of  claim 17 , wherein the lenses with a refractive index of from about 2.2 to about 2.6 are made of a material selected from the group consisting of zinc sulfide, zinc selenide, arsenic trisulfide, and amtir 1 . 
   
   
     19. The infrared imaging optical system of  claim 17 , wherein the lenses with a refractive index of from about 1.35 to about 2.0 are made of a material selected from the group consisting of sapphire, spinel, barium fluoride, calcium fluoride, magnesium fluoride, and magnesium oxide. 
   
   
     20. The infrared imaging optical system of  claim 17 , wherein the detector is operable in a 2–7 micrometer wavelength range. 
   
   
     21. The infrared imaging optical system of  claim 17 , further including
 a cold shield around the detector and having an opening therein at the pupil.